WHAT IS IDIOPATHIC HYPERSOMNIA?
Idiopathic Hypersomnia (IH), sometimes referred to as Idiopathic Hypersomnolence, is a neurological sleep/wake disorder characterised by excessive sleep and daytime sleepiness despite extraordinary amounts of good quality sleep. It is a debilitating condition often profoundly affecting work, education, and relationships. Click here for more information about symptoms and here for information about diagnosis and treatment.
Idiopathic Hypersomnia is one of the most misunderstood and under-researched sleep disorders. Many (including doctors) incorrectly think it refers to any case of excessive daytime sleepiness (EDS) that cannot be explained by another preexisting medical condition, sleep disorder or by lifestyle or behaviour. This is not correct. Idiopathic Hypersomnia is characterised by a number of symptoms and clinical features. EDS is just one of them.
IH was defined by Czech neurologist Bedrich Roth more than 60 years ago starting with his first monograph; "Narcolepsy and hypersomnia from the aspect of physiology of sleep (Narkolepsie a Hypersomnie S. Hlediska Fysiologie Spanku – 1957)" . Roth’s years of extensive research that led to his description of idiopathic hypersomnia as a separate disease entity was accepted and included in the first ICSD (International Classification of Sleep Disorders), the Diagnostic Classification of Sleep and Arousal Disorders in 1979. Since then it has been recognised as a “Rare Disease” and is included in the Genetic and Rare Diseases Information Center (GARD) register and Orphanet.
Bedrich Roth coined the term "Idiopathic Hypersomnia" in 1976 and defined two forms of the disease, Monosymptomatic and Polysymptomatic. While the terms polysymptomatic and monosymptomatic are no longer used research  supports the findings of previous studies [2,3,4,5] that show there are at least two forms of Idiopathic Hypersomnia. These studies show a subgroup of patients with “a complete form” of idiopathic hypersomnia with symptoms that are unique to this group ('complete' means they typically experience all of the key symptoms of Idiopathic Hypersomnia) 
The research suggests that ‘complete’ Idiopathic Hypersomnia is, in fact, an independent sleep disorder of ‘incomplete’ Idiopathic Hypersomnia. It also supports the findings in other studies[6,7,8] that show the clinical features of ‘incomplete’ Idiopathic Hypersomnia (previously referred to as ‘without long sleep’) are more closely related to those found in Narcolepsy without cataplexy (Type 2 Narcolepsy).
“(an) important result of this study is the confirmation of two forms of idiopathic hypersomnia: a complete one and an incomplete one..” 
Click here for our IH Brochure* and click here to read a comprehensive review of how we have gone from the identification of Idiopathic Hypersomnia to where we are now. This review is drawn from nearly 60 references, including at least 40 peer reviewed studies on Idiopathic Hypersomnia and Narcolepsy that span more than 6 decades as well as numerous personal conversations with the world's leading Idiopathic Hypersomnia researchers. If you are treating patients with Narcolepsy Type 2 (without cataplexy) or are a patient yourself you may also be interested in this review
*Our brochure was written by HA's director Michelle Chadwick and has been vetted and is endorsed by Professor Ron Grunstein, MBBS, MD, PhD, FRACP and international Idiopathic Hypersomnia researcher Professor Karel Šonka MD, DSc.
1. Sonka, K., Susta, M., and Billiard, M. Narcolepsy with and without cataplexy, idiopathic hypersomnia with and without long sleep time: a cluster analysis. Sleep Medicine. 2015; 16: 225–231.
2. Aldrich MS, The clinical spectrum of narcolepsy and idiopathic hypersomnia, Neurology 1996, 46, pp.393–401.
3. Bassetti, C., and Aldrich, M.S. Idiopathic hypersomnia. A series of 42 patients. Brain. 1997; 120: 1423–1435.
4. Billiard, M. Idiopathic hypersomnia. Neurol. Clin. 1996; 14: 573–582.
5. Billiard, M., Merle, C., Carlander, B., Ondze, B., Alvarez, D., and Besset, A. Idiopathic hypersomnia. Psychiatr Clin Neurosci. 1998; 52: 125–129.
6. Sasai-Sakuma, T., and Inoue, Y. Differences in electroencephalographic findings among categories of narcolepsy-spectrum disorders. Sleep Med 2015
7. Sasai T, Inoue Y, Komada Y, Sugiura T, Matsushima E, Comparison of clinical characteristics among narcolepsy with and without cataplexy and idiopathic hypersomnia without long sleep time. J Clin Sleep Med. 2008; 5: pp.572–578.
8. Ozaki, A., Inoue, Y., Nakajima, T., Hayashida, K., Honda, M., Komada, Y., and Takahashi, K. Health related quality of life among drug-naïve patients with narcolepsy with cataplexy, narcolepsy without cataplexy, and idiopathic hypersomnia without long sleep time. J Clin Sleep Med. 2008; 4: pp.572–578.